Bistellettazines A−C and Bistellettazole A: New Terpenyl−Pyrrolizidine and Terpenyl−Imidazole Alkaloids from a Southern Australian Marine Sponge, Stelletta sp

Case Studies in Molecular Network-Guided Marine Biodiscovery

In reviewing a selection of recent case studies from our laboratory, we revealed some lessons learned and benefits accrued from the application of mass spectrometry (MS/MS) molecular networking in the field of marine sponge natural products. Molecular networking proved pivotal to our discovery of many new natural products and even new classes of natural product, some of which were opaque to alternate dereplication and prioritization strategies. Case studies included the discovery of: (i) trachycladindoles, an exceptionally rare class of bioactive indole alkaloid previously only known from a single southern Australia sample of Trachycladus laevispirulifer; (ii) dysidealactams, an unprecedented class of sesquiterpene glycinyl-lactam and glycinyl-imide from a Dysidea sp., a sponge genera often discounted as having been exhaustively studied; (iii) cacolides, an unprecedented family of sesterterpene α-methyl-γ-hydroxybutenolides from a Cacospongia sp., all too easily mischaracterized and deprioritized during dereplication as a well-known class of sponge sesterterpene tetronic acids; and (iv) thorectandrins, a new class of indole alkaloid which revealed unexpected insights into the chemical and biological properties of the aplysinopsins, one of the earliest and more extensively reported class of sponge natural products.

Marine Natural Products from Flora and Fauna of the Western Australian Coast: Taxonomy, Isolation and Biological Activity

Marine natural products occurring along the Western Australian coastline are the focus of this review. Western Australia covers one-third of the Australian coast, from tropical waters in the far north of the state to cooler temperate and Antarctic waters in the south. Over 40 years of research has resulted in the identification of a number of different types of secondary metabolites including terpenoids, alkaloids, polyketides, fatty acid derivatives, peptides and arsenic-containing natural products. Many of these compounds have been reported to display a variety of bioactivities. A description of the compound classes and their associated bioactivities from marine organisms found along the Western Australian coastline is presented.

Trachycladindoles H–M: Molecular Networking Guided Exploration of a Library of Southern Australian Marine Sponges

A global natural product social (GNPS) molecular network guided search of a library of 960 southern Australian marine sponge extracts successfully detected a deep-water Great Australian Bight sponge, Geodia sp. (CMB-01063), as a new source of a rare class of indolo-imidazole alkaloids previously believed to be unique to a single specimen of Trachycladus laevispirulifer (CMB-03397). Chemical analysis of CMB-01063 detected the known trachycladindoles A–G (1–7), and led to the isolation, characterisation, and structure elucidation of the new trachycladindoles H–M (8–13). Structures for 8–13 were assigned on the basis of detailed spectroscopic analysis, with comparison to authentic standards of 1–7.

Marine sponges of the genus Stelletta as promising drug sources: chemical and biological aspects

Marine sponges of the genus Stelletta are well known as rich sources of diverse and complex biologically relevant natural products, including alkaloids, terpenoids, peptides, lipids, and steroids. Some of these metabolites, with novel structures and promising biological activities, have attracted a lot of attention from chemists seeking to perform their total synthesis in parallel to intensive biological studies towards new drug leads. In this review, we summarized the distribution of the chemically investigated Stelletta sponges, the isolation, synthesis and biological activities of their secondary metabolites, covering the literature from 1982 to early 2018.

Stellettapeptins A and B, HIV-inhibitory cyclic depsipeptides from the marine sponge Stelletta sp

Two new HIV-inhibitory depsipeptides, stellettapeptins A (1) and B (2), were isolated from an extract of the marine sponge Stelletta sp., collected from northwestern Australia. Structures of these cyclic nonribosomal peptides were elucidated on the basis of extensive NMR data analysis, and chemical degradation and derivatization studies. Stellettapeptins contain numerous nonproteinogenic amino acid residues and they are the first peptides reported to contain a 3-hydroxy-6,8-dimethylnon-4-(Z)-enoic acid moiety. Compounds 1 and 2 potently inhibit infection of human T-lymphoblastoid cells by HIV-1RF with EC50 values of 23 and 27 nM, respectively.

Recent advances in deep-sea natural products

Covering: 2009 to 2013. This review covers the 188 novel marine natural products described since 2008, from deep-water (50->5000 m) marine fauna including bryozoa, chordata, cnidaria, echinodermata, microorganisms, mollusca and porifera. The structures of the new compounds and details of the source organism, depth of collection and country of origin are presented, along with any relevant biological activities of the metabolites. Where reported, synthetic studies on the deep-sea natural products have also been included. Most strikingly, 75% of the compounds were reported to possess bioactivity, with almost half exhibiting low micromolar cytotoxicity towards a range of human cancer cell lines, along with a significant increase in the number of microbial deep-sea natural products reported.

Pyrrolizidine alkaloids

This review covers pyrrolizidine alkaloids isolated from natural sources. Topics include: aspects of structure, isolation, and biological/pharmacological studies; total syntheses of necic acids, necine bases and closely-related non-natural analogues.

Recent advances in deep-sea natural products

Review of deep-sea natural products covering the five-year period 2009–2013.

Synthesis and Biological Evaluation of Cremastrine and an Unnatural Analogue

In this Letter, we describe the first total synthesis of cremastrine, a pyrrolizidine alkaloid from Cremastra appendiculata, with anticholinergic activity as well as an unnatural analogue. The streamlined synthesis proceeds in 9 steps, 7 steps longest linear sequence, in 25.2% overall yield, and features novel methodology to construct the pyrrolizidine core. Biological evaluation of cremastrine and the unnatural analogue indicated that both are pan-mAChR functional antagonists.

New one-pot methodologies for the modification or synthesis of alkaloid scaffolds

There are several avenues by which promising bioactive natural products can be produced in sufficient quantities to enable lead optimization and medicinal chemistry studies. The total synthesis of natural products is an important, but sometimes difficult, approach and requires the development of innovative synthetic methodologies to simplify the synthesis of complex molecules. Various classes of natural product alkaloids are both common and widely distributed in plants, bacteria, fungi, insects and marine organisms. This mini-review will discuss the scope, mechanistic insights and enantioselectivity aspects of selected examples of recently developed one-pot methods that have been published in 2009 for the synthesis of substituted piperidines, quinolizidines, pyrrolidines, hexahydropyrrolizines, octahydroindolizines and γ-lactams. In addition, progress on the synthesis of β-carboline (manzamine) alkaloids will also be discussed.

Synthesis of (+/-)-bistellettadine A

Esterification of the trienoic acid with o-xylylene dibromide gave the bis ester that underwent a templated Diels-Alder reaction to afford the macrodiolide stereospecifically in a single step. The synthesis of bistellettadine A was completed in four steps by hydrolysis and side chain elaboration.

Discorhabdins revisited: cytotoxic alkaloids from southern australian marine sponges of the genera Higginsia and Spongosorites

Chemical analysis of southern Australian marine sponges of the genera Higginsia and Spongosorites has yielded examples of the discorhabdin class of alkaloids. These include the known metabolites (+)-discorhabdin A (1), (+)-discorhabdin D (2), makaluvamine J (6), and damirone A (7), together with four new analogues, (+)-dihydrodiscorhabdin A (3), (+)-debromodiscorhabdin A (4), (+)-dihydrodiscorhabdin L (8), and (+)-discorhabdin X (5), with the latter compound being the first reported example of a thio heterocycle flanked by oxo-thio-acetal and azo-thio-acetal functionalities. Structures for the new compounds were assigned on the basis of detailed spectroscopic interpretation.